This invention relates to an optical amplifier. Optical amplifiers are devices useful to optically (i.e., without conversion to electrical or other signal types) amplify light signals being propagated through a fiber optics line.
In particular, so-called "on fiber" amplifiers are known wherein the amplifier element comprises a section of an active light guide as obtained by a doping process using special substances (typically rare earths); in going through that light guide section, the optical signal is amplified by pumping light energy from laser sources.
Occasionally, the amplification is split between two amplification stages, that is, two discrete sections of the active light guide. Two-stage optical amplifiers have been known, for instance, from U.S. Pat. No. 5,115,338 and European Patent Application EP 0509577.
The implementation of optical amplifiers, especially two-stage ones, poses space problems. In fact, the active light guide sections often have to be comparatively long--up to several tens of meters in length--and cannot be convoluted to less than a minimum bending radius for fear of attenuating the signal or possibly damaging the light guide beyond repair. In addition, the amplifier is to accommodate a number of optical, electronic, and electrical components. Lastly, several interconnection light guide sections must be provided between the various components which require to be sufficiently long; indeed, light guide splicing problems are likely to be encountered (during the amplifier assembly process), whereby some light guide excess length must be conceded to allow for reiterate splicing of a light guide.
Further, the splicing operation requires that purposely designed equipment be operated close to the amplifier outer case, on the exterior thereof for space reasons; also on this account, a sufficient length of the light guide should be made available fop use as a starter to said equipment during the assembly process.
In the field of devices attendant to fiber optics lines, joining devices are known--particularly intended for light guides including a large number of individual fibers--which address the problem of providing for a rational layout of the light guide allowance within a case. Devices of this kind are known, for instance, from U.S. Pat. Nos. 4,428,645; 4,679,896; 4,687,289 and 4,619,499.
It should not be overlooked, however, that the problems affecting the joining devices differ from those of optical amplifiers. In fact, the joints include no other optical or electrical components besides the light guide, whereby the difficulties inherent to the mutual optical connection of several components, as are typical of an optical amplifier, are non-existent. Further, the demand fop compact size is mope stringent on an optical amplifier, despite this being a much more complicated construction than a joint; indeed, whereas a joint is normally a stand-alone component somewhere along a light guide, an amplifier requires to be housed inside a cabinet or a cabin together with other components.
In a typical arrangement including a single amplification stage, an optical amplifier would comprise a section of an active light guide, a dichroic coupler, a pump laser source arranged to act on the active light guide section through the dichroic coupler, a directional coupler associated with a respective optical meter, and light guide sections interconnecting the various components.
Where plural amplification stages are used, the number of the components would increase; as an example, in a typical two-stage arrangement, the optical amplifier would comprise two sections of active light guide, two dichroic couplers, two directional couplers associated with two respective optical meters, and light guide sections interconnecting the various components.